The present application is based on, and claims priority from, Japanese Patent Application No. 2004-275836, filed on Sep. 22, 2004, the contents of which are hereby incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to an image-pickup apparatus and a camera having the same, including an image-pickup device, a display device for displaying an image picked up by the image-pickup device and an auto focus arithmetic control unit.
2. Description of Related Art
Conventionally, as to a camera, such as a digital camera, including an image pickup device and a display means for displaying an image picked up by the image pick device, there is known a camera having a reading mode for reading an image relatively fast by way of reading a certain portion of the image in order to provide faster auto focus control and an appropriate preview display while an auto focus control is performed, and updating and displaying the read certain portion of the image as a preview display (e.g., Japanese patent publication laid-open No. 2004-023747).
A CCD is employed as an image-pickup device in most digital cameras. Such a camera is configured to carry out auto focusing according to image information obtained by a CCD. There exists a “mountain-climbing-scan method” in a conventional art for auto focusing by way of a CCD driving method. An exclusive driving mode is known for performing fast auto focusing with the mountain-climbing-scan method. According to this driving method, during focusing computation (arithmetic calculation) process for a display screen, only an area including required image data is read and an unnecessary area is flashed and transferred fast (fast flashing transfer). Normally, a screen is vertically divided into three areas: an upper area; a middle area; and a lower area. The middle area is configured to be an area to be read, and the upper and lower areas are configured to be areas to be fast flashed. Such a driving method has an advantage where contrast information (high-frequency component information) of an object to be photographed can be obtained fast relative to a normal preview driving method, on the contrary, it has also two disadvantages as follows.
First, image data of all field of an angle of view cannot be obtained during a focusing operation with an image-pickup apparatus configured to carry out the above-described driving method. Thus, an image on a display portion such as a liquid crystal panel employed in the image-pickup apparatus cannot be updated and therefore the apparatus keep displaying the image displayed just before shifting to an auto focus operation. For instance, a camera is configured to be an apparatus required to be capable of following an object to be photographed by an operator at all time. However, in the case where renewal of the displayed image is not carried out for some seconds, it is hard for the operator to follow a moving object, and deterioration of usability of the apparatus may occur.
An increase in electrical power consumption can be a second disadvantage. This disadvantage results from that a transfer clock frequency is increased when the area unnecessary for the above calculation is fast flushed (flushed at high speed). Basically, electrical power consumption is increased especially in a focusing operation in a sequence of operations of an image-pickup apparatus because a motor is driven. Moreover, the increase in electrical power consumption at the image-pickup portion gives rise to shortening of a life of a battery employed in the apparatus.